Exhaust gas treatment systems for treating exhaust gas from an engine of a vehicle may include a particulate filter. If the engine is a diesel engine, then the particulate filter may be referred to as a diesel particulate filter. The particulate filter traps particulate matter, i.e., soot, from the exhaust gas of the engine. The particulate filter may include one or more substrates that define a plurality of apertures, through which the exhaust gas must flow. The particulate matter collects on the substrate as the exhaust gas flows through the apertures. The particulate filter is occasionally regenerated to remove the collected particulate matter. Regeneration of the particulate filter includes heating the particulate filter to a temperature sufficient to burn the collected particulate matter for a time period sufficient to completely burn all of the particulate matter off of the substrates of the particulate filter, which converts the particulate matter to carbon dioxide that dissipates into the atmosphere.
During some vehicular operating conditions, such as when the engine is operating under a very light load, the engine may consume little fuel and not generate sufficient excess heat to properly heat the particulate matter during regeneration of the particulate filter. In order to properly and completely heat the particulate matter, fuel may be added to the exhaust gas to burn upstream of the particulate filter. Accordingly, regeneration of the particulate filter may require consumption of fuel when not otherwise needed to power the vehicle. When the engine is operating under a light load, the additional fuel used to regenerate the particulate filter may be substantial. Furthermore, the rate at which the particulate matter is burnt from the particulate filter may slow during the regeneration event. As such, the amount of fuel required to burn a given quantity of particulate matter of the beginning of a regeneration event may increase toward the end of the regeneration event, further decreasing the fuel efficiency when the vehicle is regenerating the particulate filter while the engine is operating under a light load.